The present invention relates to a musical envelope-producing device and, more particularly, to a musical envelope-producing device which is employed for an electronic watch to perform melody sounds at a predetermined time and which adds an envelope characteristic to the melody sounds.
Recently, digital electronic watches which play various melodies instead of a monotonous alarm sound at predetermined times have been commercially available. These digital electronic watches display the time digitally, and a desired time may be set by the user. A conventional electronic watch with a melody function comprises a memory circuit for storing pitch data and duration data of a melody, a pitch frequency divider and a duration frequency divider which respectively produce a pitch signal and a duration signal according to the pitch data and the duration data, an address counter for specifying a memory address of melody sound data which is stored in the memory circuit, and a speaker means for converting an electric signal to a sound signal, in addition to a known time circuit. An impedance circuit corresponding to an envelope waveform producing unit is further provided for improving the tone quality of a melody sound produced by a conventional electronic watch to be as real as possible. The impedance circuit, for example, is constituted by a parallel circuit of a capacitor and a resistor. The potential of a melody signal is controlled in accordance with a time constant determined by the capacitance of a capacitor C and the resistance of a resistor R. A continuity characteristic is added to the melody signal so that a melody sound having the desired envelope characteristic is produced.
However, in an electronic watch having an impedance circuit which functions as the conventional envelope-producing device described above, a continuity characteristic is only accomplished in a manner which independent of the duration of various notes. The time constant of the impedance circuit is fixed and an envelope characteristic in accordance with this time constant is added to the original melody sounds. In other words, a single continuity characteristic is utilized. As a result, the conventional envelope-producing device is inadequate in that an envelope characteristic particularly directed to the performance tempo of melody sounds may not be accomplished. For example, when short notes such as the thirty-second note or the sixteenth note are consecutively performed, the next sound is generated before the current sound has been sufficiently attenuated. Therefore, the distinction between the two sounds becomes unclear. On the other hand, when long sounds such as whole notes are consecutively performed, the tone is attenuated before the duration of the note reaches a predetermined length, giving the listener an artificial impression. Furthermore, since time constants of CR components vary, the musical envelope characteristic accordingly varies.